In some motor vehicles (more commonly in trucks and Sport Utility Vehicles), it has been known to have a drive train which provides switchable four-wheel drive. These systems typically have the rear wheels continuously driven by torque from the propshaft, which is driven by the transmission. These systems tend to have user-switchable four-wheel drive, such that the user through a lever (e.g., shifter, switch) engages a transfer case that redistributes a portion of the torque from the rear wheels to the front wheels. These systems are primarily designed to operate during low traction conditions, such as slippery conditions created by snow or off-road type conditions.
In other motor vehicles (more commonly in passenger cars, such as sedans), it has been known to have a drive train that provides all wheel drive (AWD). These systems typically have one set of wheels (typically the front wheels) driven by torque from the transmission and, as required, torque is redistributed to the other set of wheels (typically the rear wheels), by actuation of a clutch system. This redistribution of torque may be automatically transferred by the vehicle when it determines that the front wheels have angular velocities that differ by a predetermined amount from the angular velocities of the rear wheels, which indicates slippage of the front wheels created by torque exceeding traction. When the vehicle determines this difference in angular velocities between wheels, it engages the clutch mechanism, which couples a driveshaft to the operating power train system that redistributes some of the torque generated through the power train to the rear wheels. This system reduces the torque driven to the slipping wheels to a point to achieve traction again, and redistributes the reduced torque to the non-slipping wheels.
It would be advantageous to have a drive train system that provides driver selectable AWD capability by redistributing torque more efficiently (i.e., less power loss). It would also be advantageous to have an AWD drive train system that may be produced at a lower cost and with greater reliability than conventional AWD systems.